A long string of ex­pe­ri­ments over dec­ades have re­peat­edly found that an­i­mals aren’t as dumb as hu­mans tra­di­tion­ally thought they were and far from it. But are they act­ually con­scious?

Stud­ies have giv­en only vague glimpses of an an­swer. But some sci­en­tists have said an or­gan­ism must be con­scious if it has “ep­i­so­dic mem­o­ry.” This is ba­sic­ally the mem­o­ry of the “what, where and when” of events in life.

New re­search has found that some an­i­mals may have just this sort of mem­o­ry.

The meadow vole Mi­cro­tus penn­syl­van­i­cus, a small ro­dent that tends to hide in tun­nels un­der the grass. It is one of the most com­mon small mam­mals in North Amer­i­ca. (Im­age cour­te­sy U.S. Nat'l Park Serv­ice)

Ro­dents known as mead­ow voles can “re­call the ‘what,’ ‘where,’ and ‘when’” of a past ev­ent, re­search­ers wrote in the ti­tle of a new study pub­lished in the re­search jour­nal An­i­mal Cog­ni­tion.

Al­though past stud­ies had sug­gested such abil­i­ties in an­i­mals, they in­volved put­ting the crea­tures through tests that in­volved some train­ing, the au­thors said. That opened the re­sults to crit­i­cism that the train­ing could have af­fect­ed their be­hav­ior in some way that made the an­i­mals merely act as though they knew “what, where and when.” The new study in­volved no pre-train­ing.

It ex­ploited the fact that fe­male voles, along with some oth­er an­i­mals, en­ter a pe­ri­od of peak sex­u­al re­cep­ti­vity just af­ter giv­ing birth. The some­what sur­pris­ing ten­den­cy may be ex­plained by the crea­tures’ short life­span, which com­pels them to pack a lot of re­pro­duc­tion in­to lit­tle time, said bi­ol­o­gist Mi­chael H. Fer­kin of the Un­ivers­ity of Mem­phis, Tenn., the stu­dy’s lead au­thor.

Male voles seem to be aware of the females’ pat­tern of re­cep­ti­vity.

In one ex­pe­ri­ment, Fer­kin and col­leagues briefly put male voles in a cage that con­tained two cham­bers. One cham­ber con­tained a fe­male that was a day away from giv­ing birth. The oth­er con­tained a fe­male that was sex­u­ally ma­ture, but not due to be in a state of height­ened re­cep­ti­vity an­y­time soon.

A day lat­er, the males were placed in the same ap­pa­rat­us, which was now emp­ty and clean. The males in­i­tially “chose and spent sig­nif­i­cantly more time in­ves­ti­gat­ing the cham­ber that orig­i­nally housed the preg­nant fe­ma­le”—who would by now have en­tered peak re­cep­ti­vity, the re­search­ers wrote.

This sug­gested, they continued, that the males both re­called and used key in­for­ma­tion from the ear­li­er event: what was in the cage, where and when.

Un­der slightly al­tered con­di­tions, male voles showed no pref­er­ence for ei­ther side of the cage, they wrote. For in­stance, when only half an hour had passed since the in­i­tial ex­po­sure to the fe­ma­les, there was no pref­er­ence ap­par­ent. Nor were there any in cases in which a day had passed, but where the in­i­tial en­coun­ter was dif­fer­ent—with a peak-re­cep­ti­vity fe­male re­plac­ing the preg­nant fe­ma­le. The peak-re­cep­ti­vity fe­male would no long­er be in that state a day lat­er.

“The re­sults of these and ad­di­tion­al ex­pe­ri­ments sug­gest that male voles may have the ca­pa­city to re­call the ‘what,’ ‘where,’ and ‘when’ of a sin­gle past event,” Fer­kin and col­leagues wrote in the pa­per, pub­lished in the jour­nal’s July 26 ad­vance on­line is­sue. This know­l­edge “may al­low males to re­mem­ber the loca­t­ion of fe­males who would cur­rently be in height­ened states of sex­u­al re­cep­ti­vity.”

The work “ap­pears to be a very thor­ough and care­fully done piece of re­search that makes a sol­id con­tri­bu­tion,” wrote psy­chol­o­gist Bill Roberts of the Un­ivers­ity of West­ern On­tar­i­o in Lon­don, On­tar­i­o, in an e­mail. “The con­trols used are im­pres­sive.” Roberts had ar­gued in a 2002 pa­per that re­search up to then sug­gested an­i­mals have no sense of time.

Fer­kin’s study does make at least one “ma­jor as­sump­tion,” Roberts added: that the males some­how know that the late-preg­nant fe­males will be re­cep­tive 24 hours lat­er. Anoth­er pos­si­ble problem, Fer­kin and col­leagues them­selves wrote, is that the ro­dents may just know how to make de­ci­sions based on how viv­id or faint a mem­o­ry is—with­out un­der­stand­ing that this de­pends on how much time has passed. In oth­er words, they might lack a real con­cept of time.

University of Tor­onto mem­ory re­search­er End­el Tulv­ing cited an­other, “mi­nor” quib­ble with the study. Voles have a very keen sense of smell, he noted. Per­haps—un­be­knownst to the hu­mans—even in cleaned, dis­in­fected cages, the ro­dents could sniff some­thing that cues their act­ions.

But overall, the find­ings add to a body of work sug­gesting an­i­mals have a ca­pa­city for “men­tal time trav­el,” Roberts wrote. For in­stance, past work sug­gested some apes can an­ti­cipate a fu­ture need for tools, and scrub jays re­mem­ber what kind of food they stored, where and when.